Many organizations have multiple computer networks that include tens of thousands of hosts such as desktop computers, servers, gateways, routers, printers, televisions, cell phones, and so on. These hosts communicate with one another by sending messages that are typically divided into packets of information. A source host sends a packet to a destination host by specifying that the packet is to be delivered to the address of the destination host. Most computer networks are Internet Protocol (“IP”) networks that employ an Internet Protocol (“IP”) addressing scheme to address hosts such as IP version 4 (“IPv4”) or IP version 6 (“IPv6”). IPv4 specifies an IP address of 32 bits that is divided into a network address portion and a host address portion. IPv4 addresses are typically represented by four numbers that vary from 0 to 255 separated by periods such as “10.168.1.1.” IPv4 originally allowed the network address portion to be 8, 16, or 24 bits, referred to as class A, B, or C IP addresses, respectively. The combination of IP address and class uniquely identifies a host, which is represented as “10.168.1.1/B” for an IPv4 class B address. Because these three network address sizes meant that many host addresses might go unused, IPv4 was updated to employ the Classless Inter-Domain Routing (“CIDR”) in which the network address could vary in size from 1 to 31 bits. The combination of the IP address and the number of bits in the network address, referred to as a network address mask, uniquely identifies a host, which is represented as “10.168.1.1/20” for an IPv4 address with a 20 network address. The 32-bit IP address of IPv4 was thought at one time to be large enough to uniquely identify all hosts of each network. Because of the rapid growth of the Internet and computer networks for both organizations and individuals, a 32-bit IP address proved to be not large enough. IPv6 was developed to overcome the 32-bit limitation of IPv4. IPv6 specifies that an IP address has 128 bits and can thus address over 1028 more addresses than IPv4.
An organization may modify the configuration of its networks from time to time to meet its changing needs. For example, the organization may add new hosts, upgrade operating systems, install new applications, and so forth on its existing networks and may even create new networks or sub-networks. Although system administrators try to keep accurate records of the configuration of the network, referred to as a “network map,” the task of keeping such records is time-consuming and error-prone in part because of the large number of hosts and applications and the large number of modifications made to the network over many years.
Many automated tools have been developed to assist a system administrator in generating and updating a network map, especially for IP networks. To learn the configuration of hosts, some tools send messages to the hosts using Simple Network Management Protocol (“SNMP”). An SNMP-enabled host responds to requests for configuration information. When a host receives from a requesting host an SNMP request message that is addressed to it, the host retrieves the requested configuration information (referred to as a variable) and sends to the requesting host a response message that includes the configuration information. A tool that employs SNMP may be provided an IP address of a target host and sends a series of requests to that target host to obtain the configuration information of that target host. One well-known tool is Nmap, which probes a computer network to extract various types of configuration information. For example, Nmap can scan a range of IP addresses to discover hosts within that range, scan for open ports on a host, and retrieve system configuration information such as identifying the operating system of a host.
Although these automated tools help simplify the task of generating a network map, the task of generating a network map for large networks can be very difficult for several reasons. For example, a network administrator may not even know what ranges of IP addresses are used by a network. Without knowing these ranges, the process of host discovery may be very slow as a very large range of IP addresses may need to be checked. Moreover, the network traffic needed to check so many IP addresses may place an unacceptable burden on the network. As another example, a network administrator may need to run many different tools to get as complete a network map as possible. Because of the complexity of the tools and the computer networks, it can be difficult for a network administrator to keep track of what tools to run, when to run the tools, and in what order to run the tools. It would be desirable to have a tool that would help overcome these difficulties.